144 research outputs found
Terahertz Waveguiding in Silicon-Core Fibers
We propose the use of a silicon-core optical fiber for terahertz (THz)
waveguide applications. Finite-difference time-domain simulations have been
performed based on a cylindrical waveguide with a silicon core and silica
cladding. High-resistivity silicon has a flat dispersion over a 0.1 - 3 THz
range, making it viable for propagation of tunable narrowband CW THz and
possibly broadband picosecond pules of THz radiation. Simulations show the
propagation dynamics and the integrated intensity, from which transverse mode
profiles and absorption lengths are extraced. It is found that for 140 - 250
micron core diameters the mode is primarily confined to the core, such that the
overall absorbance is only slightly less than in bulk polycrystalline silicon.Comment: 6 pages, 3 figures, journal submissio
Preparation, characterization, and electrical properties of epitaxial NbO2 thin film lateral devices
Epitaxial NbO2 (110) films, 20 nm thick, were grown by pulsed laser
deposition on Al2O3 (0001) substrates. The Ar/O2 total pressure during growth
was varied to demonstrate the gradual transformation between NbO2 and Nb2O5
phases, which was verified using x-ray diffraction, x-ray photoelectron
spectroscopy, and optical absorption measurements. Electric resistance
threshold switching characteristics were studied in a lateral geometry using
interdigitated Pt top electrodes in order to preserve the epitaxial crystalline
quality of the films. Volatile and reversible transitions between high and low
resistance states were observed in epitaxial NbO2 films, while irreversible
transitions were found in case of Nb2O5 phase. Electric field pulsed current
measurements confirmed thermally-induced threshold switching.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Journal of Physics D: Applied Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at http://dx.doi.org/10.1088/0022-3727/48/33/33530
Multidimensional Coherent Spectroscopy of a Semiconductor Microcavity
Rephasing and non-rephasing two-dimensional coherent spectra map the
anti-crossing associated with normal-mode splitting in a semiconductor
microcavity. For a 12-meV detuning range near zero detuning, it is observed
that there are two diagonal features related to the intra-action of
exciton-polariton branches and two off-diagonal features related to coherent
interaction between the polaritons. At negative detuning, the lineshape
properties of the diagonal intra-action features are distinguishable and can be
associated with cavity-like and exciton-like modes. A biexcitonic companion
feature is observed, shifted from the exciton feature by the biexciton binding
energy. Closer to zero detuning, all features are enhanced and the diagonal
intra-action features become nearly equal in amplitude and linewidth. At
positive detuning the exciton- and cavity-like characteristics return to the
diagonal intra-action features. Off-diagonal interaction features exhibit
asymmetry in their amplitudes throughout the detuning range. The amplitudes are
strongly modulated (and invert) at small positive detuning, as the lower
polariton branch crosses the bound biexciton energy determined from negative
detuning spectra.Comment: 13 pages, 4 figure
Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3
Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in
thickness, of the topological insulator Bi2Se3 revealed a strong dependence of
the carrier relaxation time on the film thickness. For thicker films the
relaxation dynamics are similar to those of bulk Bi2Se3, where the contribution
of the bulk insulating phase dominates over that of the surface metallic phase.
The carrier relaxation time shortens with decreasing film thickness, reaching
values comparable to those of noble metals. This effect may result from the
hybridization of Dirac cone states at the opposite surfaces for the thinnest
films
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